Exercise generally, and aerobic exercise in particular, is of value to individuals because it conditions and improves respiratory and circulatory systems. Exercise is characterized in part by intensity and duration. Intensity, which may be thought of as the effort expended by an individual, is reflected in the individual's physiological condition. For example, heart rate, breathing and metabolism increase with exercise intensity, and are referred to herein as the "physiological indicators of intensity."
While exercise intensity is a physiological phenomenon and is properly measured by one of the physiological indicators, it is also manifested outside the body by an individual's physical movement or by the physically measurable work performed by the individual. For example, at a fixed level of resistance, pedal rpm on stationary exercise bicycle gives some indication of the individual's level of exercise intensity. This type of indication is referred to herein as an externally observable "physical indicator of intensity."
While physical indicators of intensity such as ergometers or tachometers are easier to implement than physiological indicators of intensity, their usefulness is limited because of the subjective nature of exercise. For example, two persons riding a stationary bicycle at the same levels of speed and resistance would appear to have the same level of exercise intensity based externally observable physical indicators, such as pedal rpm. Depending upon each person's level of fitness, their respective actual levels of exercise intensity (as measured by one of the physiological indicators) could be quite different.
For effective aerobic exercise, it is necessary that physiological intensity reach a certain minimum threshold. At the same time, if exercise is too intense, it becomes primarily anaerobic (i.e., oxygen depleting). Exercise at an excessive level of intensity does not yield additional improvements in the body's aerobic fitness.
Thus, between the upper and lower thresholds of training intensity lies the aerobic training range. It is important, therefore, to monitor levels of intensity to ensure that intensity falls within this training range. To monitor intensity, a number of physiological conditions may be inspected, including heart rate, breathing as a percentage of maximal oxygen intake, and metabolism.
Typically, such monitoring requires a sensor which is placed in physical contact with an individual to measure the individual's heart rate or the like. The individual can then be apprised of his or her level of exercise intensity. One simple example of this is someone on a stationary exercise bicycle who takes his or her own pulse after a workout to determine whether he or she has reached a sufficient level of aerobic intensity.
A more sophisticated approach, however, is to employ biofeedback techniques for periodically adjusting workout intensity in response to the physiological indicators of intensity, such as heart rate. Examples of such devices are provided in U.S. Pat. Nos. 3,395,698 and 3,744,480. While theoretically any of the physiological indicators may be used, it is most practical to use heart rate, and therefore the examples set forth herein all use heart rate as the physiological indicator of intensity.
Devices which employ biofeedback techniques include exercise bicycles having variable load resistance to pedal movement. This resistance can be provided by well-known mechanical and electrical devices, including alternators, which can be coupled by chains or belts to the pedals.
In such devices, a heart rate detector is coupled to the user, typically by an ear clip. A target heart rate is selected, either by the user or automatically by the device. As the user exercises, his or her pulse is periodically measured and compared to the target heart rate. If the user's heart rate is below the target, the load resistance is increased. Likewise, if the user's heart rate is above the target heart rate, the load resistance is decreased.
In this manner, these exercise devices function as "biofeedback-type systems." They adjust load resistance as a function of heart rate to establish and maintain the user's heart rate (i.e., physiological exercise intensity) at or near the desired or target level. For a variety of reasons, these devices have been less than optimal.
Specifically, for effective operation, these systems depend on the continuous availability of heart rate data. For example, if the user wears an ear clip, heart rate data is available throughout the exercise.
There have, however, been recent advances in heart rate detection technology, such as disclosed in U.S. patent application Ser. No. 07/722,800 filed Jun. 28, 1991 (assigned to the assignee of this application) and incorporated herein by reference. Unlike older heart rate detection techniques which required cumbersome ear clips or the like, this new detection technology measures a user's heart rate whenever his or her hands are placed on the exercise device's handgrips. Such handgrips, for example, can be located on the handlebars of an exercise bicycle.
One disadvantage, however, of locating the detectors on the handgrips in a heart rate measurement system is that the user will tend to remove his hands from the handgrips from time to time. When the user's hands are removed, the biofeedback-type device will receive no information about the user's heart rate. To be practical, a heart rate management system should continue to operate effectively even when the flow of heart rate data is interrupted for periods as long as ninety seconds. Existing systems are not designed to handle the intermittent availability of heart rate signals.
Moreover, it has come to be appreciated that systems should not only be able to process intermittent heart rate data, but in fact periodically should also invite users to remove their hands from the handgrips (or otherwise disengage the sensor). In this manner, the user does not feel "chained" to the heart rate measuring device, and is free to wipe his or her brow, turn the pages of a book, adjust a personal tape player, or do any of the many things people riding an exercise bicycle are likely to do to divert their attention from an otherwise boring exercise.
As explained above, externally observable indicators of exercise intensity (such as pedal speed) are related to the user's actual physiological level of exercise intensity, but are of limited value as tools for measuring that intensity because they are not calibrated for each individual user. Consequently, biofeedback-type devices of the past have relied on heart rate, and have not utilized external indicators (such as pedal rpm) in conjunction with physiological data to attain the highest possible performance.
Also, in some existing devices, load changes tend to be too abrupt and too frequent. Preferably, for most people load changes should be gradual. On the other hand, it may be desirable to make load changes more dramatic for persons in better physical condition. It is also desirable that the device should anticipate changes in the user's heart rate so that load can be adjusted earlier, and therefore more gradually.